The invention relates to a system for supplying fuel to an internal-combustion engine which is arranged in an engine compartment, a forward-flow fuel pipe, which starts from a fuel tank situated outside the engine compartment and has a pump, leading to the internal-combustion engine, and a pressure regulator being provided which connects a branch pipe branching off the forward flow pipe with a return-flow pipe leading to the fuel tank in order to adjust a desired fuel pressure in the forward-flow pipe.
From the DE 39 14 939 A1, for example, such a system for supplying fuel to an internal-combustion engine is known. In this case, the pressure regulator is arranged close to the internal-combustion engine or close to the fuel injection valves which are fastened to the internal-combustion engine suction system and branch off from the engine-compartment-side end of the forward-flow pipe. Normally, much more fuel flows through the forward-flow fuel line than will finally be required in the internal-combustion engine because the fuel volume flow is determined by the normal constant delivery output of the pump. In this case, the pump delivery output is dimensioned such that a sufficient amount of fuel is available in all possible internal-combustion engine operating points and particularly also in the operating point of the maximal nominal output. In partial-load operating points, a relatively large excess fuel volume flow is therefore available which arrives back in the fuel tank by way of the return-flow pipe. In this case, the pressure regulator adjusts the volume flow arriving in the return-flow pipe in such a manner that a defined fuel pressure exists in the forward-flow pipe. In this case, this excess fuel pressure may be defined either with respect to the ambient pressure or with respect to the pressure conditions in the suction system.
In normal internal-combustion engine operation, as indicated in the above description, a considerable amount of fuel is always transferred by pumping by way of the forward-flow and the return-flow pipe. In this case, this transferred fuel amount always travels through the engine compartment which is warmed up by the waste heat of the internal-combustion engine. This causes not only a heating of the fuel flow that was transferred by pumping but also results in a temperature rise of the whole fuel volume contained in the fuel tank. However, this rise in temperature is undesirable because easily volatile fuel constituents will then tend to evaporate.
It is therefore an object of the invention to provide measures by means of which a heating particularly of the fuel volume situated in the fuel tank by the engine compartment waste heat is largely prevented.
For achieving this object, it is provided that the branch pipe leading from the forward-flow pipe by way of the pressure regulator to the return-flow pipe as well as the pressure regulator are arranged outside the engine compartment. According further to the present invention, the branch pipe and the pressure regulator are arranged close to the fuel tank. In another preferred embodiment, the pressure regulator can be connected with the engine compartment side end of the forward-flow pipe as an alternative to the branch pipe.
According to the invention, the excess fuel flow delivered by the pump no longer travels through the engine compartment but is branched off the forward-flow pipe already outside the engine compartment. Any heating of the fuel flow returning into the fuel tank by the internal-combustion engine is therefore largely excluded. The effect according to the invention can be further increased when the branch pipe and the pressure regulator are arranged near the fuel tank. Preferably, the arrangement according to the invention is situated in a motor vehicle, in which case the internal-combustion engine as well as the engine compartment are housed in the front of the vehicle and the fuel tank is housed in the rear of the vehicle. If the pressure regulator as well as the branch pipe are then also arranged in the vehicle rear, a heating by ambient influences will then also be almost impossible. Although a fuel system for a motor vehicle is known from German Patent Document DE-OS 28 41 557, in the case of which the pressure regulator is also arranged on the fuel tank, in this known fuel system, the complete fuel quantity delivered by the pump always arrives in the engine compartment by way of the forward-flow pipe so that this will again result in a heating of the fuel flow returned by way of the pressure regulator. In the case of this known solution, a branch pipe does not exist which branches off the forward-flow pipe outside the engine compartment and by way of the pressure regulator lead into the return-flow pipe.
In order to exclude hot-start problems which may occur under the least favorable marginal conditions with a system according to the invention for the fuel supply according to the present invention, the pressure regulator may, as an alternative to the branch pipe, be connectable with the engine-compartment side end of the forward-flow pipe. This connection between the pressure regulator and the engine-compartment-side end of the forward-flow pipe will then be established for a short time at the start of the internal-combustion engine in order to intensively rinse the engine-compartment-side end of the forward-flow pipe from which the fuel injection nozzles branch off, and thus remove any possible fuel vapor bubbles. When this rinsing operation is completed, the branch pipe, which branches off from the forward-flow pipe outside the engine compartment and particularly close to the fuel tank, is connected again with the pressure regulator, and the connection between the pressure regulator and the engine-compartment-side end of the forward-flow pipe is interrupted. For this purpose, a simple reversing valve may be provided. Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.